Image processing method, image processing device, image processing program, and recording medium for recording image processing program

ABSTRACT

The image processing device is configured including: a Y/C separator section for separating image data into chromaticity data BY xy , RY xy  and luminosity data YY xy ; a chromaticity noise removing section for smoothing the chromaticity data BY xy , RY xy ; a luminosity noise removing section for smoothing the luminosity data YY xy ; and a noise-removing-rate computing section for computing a distribution parameter DP representative of a variation of the luminosity data YY xy  in two-dimensional coordinate space and computing, for each unit area of an image, a rate of the smoothing of the chromaticity data BY xy , RY xy  and a rate of the smoothing of the luminosity data YY xy  according to the distribution parameter DP as outputs to the chromaticity noise removing section and the luminosity noise removing section respectively. The image processing device can execute image processing on digital image data to reduce a coarse look caused by film particles without blurring edges in the image.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/915,532 filed on Jul. 27, 2001, currently pending. The disclosure ofU.S. patent application Ser. No. 09/915,532 is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing method, an imageprocessing device to carry out the image processing method, and arecording medium to record a program implementing the image processingmethod, whereby the quality of an image produced on photosensitivematerial from digital image data is improved by reducing particle noisethat cause a coarse look of the image without blurring the edges in theimage.

2. Discussion of the Related Art

Conventionally, photographs have been printed by analog exposure wherebylight is projected onto a photographic film recording having an originalimage thereon, so that the light having passed through that photographicfilm illuminates photographic printing paper. Another popular method inrecent years is digital exposure whereby monochromatic red, green, andblue lights are projected on each pixel on photographic printing paperfor printing on the basis of digital image data obtained by scanning animage on a photographic film with a scanner or the like or by takingphotographs with a digital camera, etc.

In a photographic printing device for carrying out digital exposure, thepixel density of an image printed on photographic printing paper isdictated by the resolution of the scanner and that of the exposure head.Particles forming an image on a positive film have a typical density ofabout 2500 dpi. Digital-exposure photographic printing devices arealready introduced to the market with the same level of resolution asthe particle density. The digital-exposure photographic printing deviceis capable of acquiring an image having the same level of resolution asthe particle density of a film and printing on photographic printingpaper images that are not inferior to those printed by analog exposure.

Note that the particle density of 2500 dpi is equivalent to 3445×2362pixels on a 135F-size (3.6 cm×2.4 cm) photographic film.

The photographic printing device for carrying out digital exposure canprocess image data and produces on the image such various specialeffects that an analog-exposure photographic printing device cannotproduce. One of the special effects is sharpening whereby images (forexample, those of people in the background and of facial features of aperson) have prominent edges. In the following description, more detailswill be given as to sharpening.

Sharpening is a process to form clear boundaries, i.e., edges, betweenadjacent objects in an image. Specifically, a set of data, termed aspatial filter, is used on image data to convert the image data in sucha manner to impart large luminosity differences to target pixelsconstituting an edge and their adjacent pixels. A very simple example isgiven below.

A 3×3 spatial filter is expressed as a 3×3 array, for example, 0 −1 0 −15 −1 0 −1 0where each element represents a coefficient applied to the luminosity ofone of the 3×3 pixels. Here, the middle value, 5, is the element appliedto the target pixel, and the other values are those applied to theadjacent pixels of the target pixel. The 3×3 filter is basically devisedso that its elements add up to 1.

For example, a 100×100 pixel image is subjected to the 3×3 filter 10000times, with a different pixel chosen as the target pixel each time, tosharpen the whole image.

Effects of the 3×3 filter will be described by way of a concreteexample. An image of a car, an airplane, or another object on a road,the sky, or another background as has many, what we call, monotonousparts where the image varies little in chromaticity and luminosity inthe background. As an example, the luminosities of 3×3 pixels in amonotonous part of the image are represented by a 3×3 array, 51 49 53 5250 49 48 51 47

Multiplying the elements of the 3×3 filter array and the associatedelements of the 3×3 pixel array, element by element, is equivalent toapplying the filter to the pixels. The filtered luminosities of thepixels are represented by a 3×3 array, 0 −49 0 −52 250 −49 0 −51 0Since the values of the filtered luminosity add up to 49, the value, 50,of the target pixel is now set to 49. It would be understood from thisexample that the filtering hardly changes luminosity in the monotonouspart of the image.

The luminosities of 3×3 pixels on an edge of the object are representedby a 3×3 array, for example, 10 30 70 15 50 90 20 80 85

At this part of the edge, values are low near the upper left corner andhigh near the lower right corner. Applying the 3×3 filter to the 3×3pixels, we obtain 0 −30 0 −15 250 −90 0 −80 0Since the values of the filtered luminosity add up to 35, the value, 50,of the target pixel is now set to 35.

Now moving to a new target pixel with a value, 90, which is to the rightof the target pixel, the luminosities of the 3×3 pixels are representedby a 3×3 array, for example, 30 70 85 50 90 95 80 85 90

Applying the 3×3 filter to the 3×3 pixels, we obtain 0 −70 0 −50 450 −950 −85 0Since the values of the filtered luminosity add up to 150, the value,90, of the target pixel is now set to 150. It would be understood fromthis example that the filtering changes luminosity by great amounts inthe edge part of the image.

FIGS. 11A, 11B illustrate the image data at the edge part before andafter the filtering. The illustration tells that sharpening is a processto add a spike-like amplification in FIG. 11B to the original contrastin FIG. 11A at an edge to enhance the contrast at the edge.

To sum up the description so far, the spatial filter, when used inprocessing image data, hardly changes the image data in monotonous partsof the image, but increases luminosity differences at the edges.Subjecting all the pixels of the image to this process enhances thesharpness of the whole image.

This conventional sharpening method, however, has a problem; imagesprinted on photographic printing paper will have their coarse lookexacerbated too.

The aforementioned high resolution digital-exposure photographicprinting device is capable of acquiring an image having practically thesame level of resolution as the particle density of a film. Aphotograph, if printed on the same scale as the photographic film, ismade of pixels, each as large as a film particle. The film particlesshare among them very similar, but not completely identical, coloringproperties and cause fine variations in chromaticity and luminosity. The“noise” occurring in the film particle level (hereinafter, will bereferred to as film particle noises) is passed on in the course ofprinting, causing a coarse look of the printed photograph.

The greater the proportion relative to the image acquired from aphotographic film is by which a photograph is scaled up in the course ofprojection and printing on photographic printing paper, the moredistinct the film particle noise of the resultant photograph appears.

In short, the conventional sharpening method exacerbates the particulatenature of the photographic film, as well as enhances edges in an image,imparting a more coarse look to the image printed on photographicprinting paper. The resultant image may look very ugly. Image qualitydegrades, especially, if human skin gives a rough look.

The following will describe sharpening as a cause of the exacerbation offilm particle noise by way of a concrete example. An example of 3×3pixels is given having luminosities represented by a 3×3 array, 45 45 4545 90 45 45 45 45where the middle value, 90, is film particle noise.

Applying the 3×3 filter to the 3×3 pixels, we obtain 0 −45 0 −45 450 −450 −45 0Since the values of the filtered luminosity add up to 270, the value,90, of the target pixel is now set to 270. It would be understood fromthis example that the filtering exacerbates the noise by a fairly greatamount.

To address this problem, we need a process whereby sharpening can becarried out without accompanying exacerbation of a coarse look, whichcould be otherwise caused by film particles. A simple method toimplement this is blurring, that is, a repeated process of replacing avalue of a target pixel with a mean value of its surrounding pixelsuntil the process covers the whole image. The blurring process, however,goes too far and blurs edges which are exactly where we wanted toincrease sharpness in the first place.

A possible alternative is to implement a blurring process on acquiredimage data before sharpening. In this case, however, the image will bestripped of its minute details.

SUMMARY OF THE INVENTION

The present invention has an objective to provide an image processingmethod, an image processing device to carry out the image processingmethod, an image processing program to implement the image processingmethod, and a recording medium to record the image processing program,all for use to produce an image on photosensitive material from digitalimage data, whereby the produced image has less of a coarse look causedby film particles and has no edges blurred.

To achieve the objective, an image processing method in accordance withthe present invention is characterized in that it includes the steps of:

-   -   separating image data into luminosity data and chromaticity        data; and    -   changing a rate of smoothing of the chromaticity data and a rate        of smoothing of the luminosity data according to a variation of        the luminosity data in two-dimensional coordinate space.

Film particle noise contains fine chromaticity variations and fineluminosity variations, i.e., chromaticity noise and luminosity noise. Inview of this, in the foregoing method, chromaticity noise removal andluminosity noise removal can be carried out at different rates toachieve optimum noise removal: for example, chromaticity noise removalis carried out at a relatively high rate where chromaticity noise isdistinctly visible, and luminosity noise removal is carried out at arelatively low rate where luminosity noise is distinctly visible.

The chromaticity variations and luminosity variations are either verysmall or practically ignorable in monotonous parts of the image andrelatively large at edges in the image; the latter variations areparticularly large at edges. Therefore, luminosity data contains moreedge information of the image than does chromaticity data. This isanother reason why it is preferable to carry out chromaticity noiseremoval and luminosity noise removal at different rates.

Another reason for this is that the human eye is more sensitive toluminosity variations than to chromaticity variations.

To retain edges in the image without blurring them, neither luminositynoise removal nor chromaticity noise removal is carried out at theedges. More preferably, since more edge information is found in theluminosity data than in the chromaticity data, the rate of luminositynoise removal should be lowered gradually to 0, but more quickly thanthe chromaticity noise removal, as moving from monotonous parts towardedges in the image. The chromaticity noise removal does not as muchattenuate edge information as the luminosity noise removal and thereforebetter reduces the coarse look of the image when carried out up to quitenear the edges.

For these reasons, the foregoing method, whereby the rates of smoothingof the chromaticity data and of smoothing of the luminosity data arechanged according to a variation of the luminosity data intwo-dimensional coordinate space, can strike the best balance betweenthe chromaticity noise removal by means of smoothing of the chromaticitydata and the luminosity noise removal by means of smoothing of theluminosity data and produce satisfactory results in both the retainmentof the edges in the image and the elimination of the coarse look of theimage.

To achieve the objective, an image processing device in accordance withthe present invention is characterized in that it includes:

-   -   (1) a data separator section for separating image data into        luminosity data and chromaticity data;    -   (2) a chromaticity noise removing section for smoothing the        chromaticity data;    -   (3) a luminosity noise removing section for smoothing the        luminosity data; and    -   (4) a smoothing rate computing section for computing a variation        of the luminosity data in two-dimensional coordinate space and        computing, for each unit area of an image, a rate of the        smoothing of the chromaticity data and a rate of the smoothing        of the luminosity data according to the variation as outputs to        the chromaticity noise removing section and the luminosity noise        removing section respectively.

In the configuration, the smoothing rate computing section computeswell-balanced rates of the smoothing of the chromaticity data and thesmoothing of the luminosity data for each unit area of the image andtherefore effectively reduces the coarse look of the image withoutblurring the edges.

The chromaticity noise removing section receives chromaticity data fromthe data separator section and the rate of chromaticity noise removalfrom the smoothing rate computing section to smooth the chromaticitydata for each unit area of the image.

The luminosity noise removing section receives luminosity data from thedata separator section and the rate of luminosity noise removal from thesmoothing rate computing section to smooth the luminosity data for eachunit area of the image.

Thus, the image has its quality greatly enhanced with better contrast,less of the coarse look, and retained sharpness of the edges.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a block diagram showing a configuration of a blurring sectionin an image processing device in accordance with the present invention.

FIG. 2 is a block diagram schematically showing a configuration of amain part of the image processing device.

FIG. 3 is an explanatory drawing showing unit areas of an image that actas repetition units in the smoothing of chromaticity data and luminositydata.

FIG. 4 is a graphical representation of an example algorithm toimplement the smoothing of chromaticity data and luminosity data.

FIG. 5 is a photograph, submitted in place of a drawing, showing anoutput of image data subjected to neither chromaticity noise removal norluminosity noise removal.

FIG. 6 is a photograph, submitted in place of a drawing, showing anoutput of the same image data as used for FIG. 5, but subjected tochromaticity noise removal.

FIG. 7 is a photograph, submitted in place of a drawing, showing anoutput of the same image data as used for FIG. 5, but subjected to bothchromaticity noise removal and luminosity noise removal.

FIG. 8 is a photograph, submitted in place of a drawing, showing anoutput of the same image data as used for FIG. 5, but enlarged andcropped near the inner end of the left eye.

FIG. 9 is a photograph, submitted in place of a drawing, showing anoutput of the same image data as used for FIG. 6, but enlarged andcropped near the inner end of the left eye.

FIG. 10 is a photograph, submitted in place of a drawing, showing anoutput of the same image data as used for FIG. 7, but enlarged andcropped near the inner end of the left eye.

FIGS. 11A, 11B are explanatory figures illustrating luminosityvariations at an edge in an image before and after sharpeningrespectively.

FIG. 12 is a flowchart showing an image processing method in accordancewith the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe an embodiment of the present invention inreference to FIG. 1 to FIG. 12.

Typically, the human eye is more sensitive to luminosity variations thanto chromaticity variations. A combination of powerfulchromaticity-noise-removing blurring (smoothing) and softluminosity-noise-removing blurring (smoothing) removes much of the noiseand retains clear edges. Understanding these characteristics of the eyeprovided the basis for the first insight that led us successfully to thepresent invention.

At edges, luminosity variations are more visible than chromaticityvariations. We can deduce from this fact that luminosity data containsmore edge information than does chromaticity data and that the edgeinformation is effectively retained if the blurring applied toluminosity data is restrained relatively to the blurring applied to thechromaticity data.

That said, applying powerful blurring to chromaticity data and softblurring to luminosity data uniformly across the entire image does notenhance the sharpness of the image very much, since such blurring takesno edge information into account. This problem is addressed byextracting areas that are considered as forming edges in the image andthen applying either restrained blurring or no blurring at all in thoseareas, while applying strong blurring to chromaticity data and softblurring to luminosity data in the other areas; this processing retainsedge information more effectively without sacrificing effectiveness innoise removal. Understanding the relationships between the blurringtechniques and the retainability of edge information provided the basisfor the second insight that led us successfully to the presentinvention.

From these insights, we have conceived an image processing method, inaccordance with the present invention, whereby film particle noise in animage data output from a scanner reading a developed photographic filmis reduced by separating the image data into luminosity data andchromaticity data and applying blurring to the chromaticity data and theluminosity data with thoroughness that is varied according to variationsof luminosity data in two-dimensional coordinate space.

We have also conceived another image processing method, in accordancewith the present invention, whereby the same goal is achieved byextracting edges from an image and removing as little noise as possibleat the edges, while, at other places, giving a priority to chromaticitynoise removal rather than to luminosity noise removal or removing alarger portion of the chromaticity noise than of the luminosity noiseaccording to variations of luminosity data in two-dimensional coordinatespace.

To start a specific description, the following will describe aconfiguration of an image processing device that implements the imageprocessing methods in accordance with the present invention.

The image processing device is configured in accordance with the presentinvention so that it can print an image on photographic printing paper(photosensitive material) by illuminating the photographic printingpaper according to, for example, BGR image data. As shown in FIG. 2, theimage processing device has an imaging section 1, an image processingsection 4 with a blurring section 2 and a sharpening section 3, and anexposure section 5.

The imaging section 1 is a scanner scanning an image (hereinafter, willbe alternatively referred to as an original image in some cases) storedon a negative film by measuring light passing through the negative film,and is configured including, for example, a light source shining lightonto the negative film, BGR color filters, and a CCD camera includingeither a single CCD (Charge-Coupled Device) or three CCDs. As lightpasses through the negative film and the color filters with resultantBGR components of the light entering the CCDs, the imaging section 1transfers electric signals to the image processing section 4 accordingto the BGR components of the incoming light. A set of image data is thusobtained which is representative of the chromaticity and luminosity ofpixels forming the original image for each of the BGR colors.

The image processing section 4 implements various kinds of imageprocessing on the BGR sets of image data transferred from the imagingsection 1, including noise removal, sharpening, compensation forirregularity in the imaging by the CCDs and in the exposure by theexposure head, gamma correction in view of the coloring properties ofthe photographic printing paper, etc. The image processing section 4 maybe provided inside the image processing device as a microprocessorand/or DSP (digital signal processor) or outside the image processingdevice as a PC (personal computer). The image processing section 4further includes a memory (not shown) temporarily storing the image datafrom the imaging section 1 and a control section (not shown) controllingthe exposure operation of the exposure section 5.

The blurring section 2, provided in the image processing section 4,includes a structure to separate the image data into luminosity data andchromaticity data and change the thoroughness of the blurring applied tothe chromaticity data and of the blurring applied to the luminosity dataaccording to the variations of the luminosity data in two-dimensionalcoordinate space. More details will be given later about the imageprocessing section 4.

The sharpening section 3, provided in the image processing section 4, isresponsive to an instruction of the operator and where necessary toproduce an image with sharp edges, implements sharpening on the imagedata from which the chromaticity and luminosity noise has been removedby the blurring section 2. Alternatively, the image data output from theimaging section 1 may be fed first to the sharpening section 3 forsharpening and then to the blurring section 2 for noise removal. Nomatter which process is implemented first, the resultant image hasbetter quality than conventional images.

Yet, if blurring is implemented after sharpening, the degree of blurringmust be adjusted according to that of sharpening to produce bestresults. In contrast, if blurring is implemented first, the degree ofsharpening requires no adjustment, making the overall operation simple.

The exposure section 5 controls exposure (inclusive of no exposure) ofphotographic printing paper for each pixel according to the BGR sets ofimage data supplied from the image processing section 4 to print animage on the photographic printing paper. Examples of means to controllight exposure include PLZT exposure heads, DMDs (digital micromirrordevices), LCDs (liquid crystal displays), LEDs (light emitting diode)panels, lasers, FOCRTs (fiber optic cathode ray tubes), and CRTs(cathodes ray tube). Needless to say, there must be provided a separatelight source to the PLZT exposure head, DMD, LCD and other control meansthat does not emit light by itself. A rotary BGR filter, as well as aprinting and other light-focus lenses, are also disposed for each colorwhere necessary.

PLZT is a (Pb_(1-x)La_(x))(Zr_(y)Ti_(1-y))_(1-x/4)O₃ solid solutionwhich is obtained by making a solid solution (PZT) of lead zirconate(PbZrO₃) and lead titanate (PbTiO₃) of a suitable ratio and addinglanthanum before subjecting it to hot-pressing. Similarly to liquidcrystal displays, PLZT can control light transmission when used incombination with a polarizer in the presence of an electric field.

The image processing device of the present embodiment has a 2167 dpiresolution and is capable of acquiring an image having practically thesame level of resolution as the particle density of the film andprinting an image on photographic printing paper.

Now, the configuration of the blurring section 2 is described in detail.As shown in FIG. 1, the blurring section 2 is made of three majorcomponents: a Y/C separator section (data separator section) 6, anoise-removing-rate computing section (smoothing rate computing section)7, and a noise removing section 8.

The Y/C separator section 6 is a block converting the BGR sets of imagedata supplied from the imaging section 1 to YCC data. The Y/C separatorsection 6 converts the BGR sets of image data to a combination ofluminosity data YY_(xy) and chromaticity data BY_(xy), RY_(xy).Characters x, y in subscript position in YY_(xy), BY_(xy), and RY_(xy)are a two-dimensional coordinate notation for pixels in a CCD in theimaging section 1.

The noise-removing-rate computing section 7 computes variations of theluminosity data YY_(xy) in two-dimensional coordinate space, or in otherwords, how the luminosity data YY_(xy) varies between different parts ofan image. Then, on the basis of the variations, it further computesrates of the blurring to be applied to the chromaticity data BY_(xy),RY_(xy) and of the blurring to be applied to the luminosity data YY_(xy)for each unit area in the image. The rates are output to the noiseremoving section 8. More specifically, the noise-removing-rate computingsection 7 discriminates between edges and other places in the image onthe basis of the variations of the luminosity data YY_(xy), so as toimplement no blurring at the edges and specify the rate of the blurringfor the chromaticity data BY_(xy), RY_(xy) greater than the rate of theblurring for the luminosity data YY_(xy) at the other places.

FIG. 3 shows an example of the design of unit areas, where the image isdivided into square unit areas each made up of 7×7 pixels with a targetpixel in the middle. Blurring is implemented for each unit area acrossthe entire image. The unit area is designed large enough to enclose asufficient number of pixels to reproduce the luminosity and chromaticityof the original image for reasons laid out immediately below.

Blurring is a process of smoothing, i.e., entirely or partiallyreplacing the chromaticity data BY_(xy), RY_(xy) and the luminosity dataYY_(xy) of a target pixel with mean values of the data over the unitarea including that target pixel. When the target pixel is distinctlydifferent from the surrounding pixels and is regarded as being noise,this process entirely or partially replaces the noise data with a meanvalue over the unit area, effectively reducing the noise.

Noise is located irregularly; however, if a very small unit area (hencevery few pixels) includes noise in it, the resulting mean data isstrongly affected by the noise. Conversely, if a very large unit area(hence very many pixels) includes noise in it, the resulting mean datais affected by two or more different noise pixels. These facts clearlyshow that the unit area does not work effectively to reduce noise if itis designed too small or too large.

Accordingly, we started with a very small unit area and graduallyincreased the number of pixels around the target pixel (hence expandedthe unit area). Results were that a tendency and irregularities startedappearing in the luminosity and chromaticity of the image when the unitarea was expanded up to 7×7 pixels. This can be likened to the minusculeBGR dots on the screen of a CRT which appear as distinct three-colorilluminated dots when viewed too close, but start forming visibleluminosity and chromaticity when moving away from the CRT and viewed ata sufficient distance for the eye to see a relatively large area. Itwill be helpful in understanding the present invention to think thatfilm particles are equivalent to those dots forming an image on a CRTscreen.

Noise in general is abnormality in luminosity and chromaticity thateither recurs (for example, stripes) or occurs in a pixel all of asudden. The noise that we would like to reduce in the present inventionis film particle noise caused by non-uniform distribution of coloringproperties of the film particles.

FIG. 8 shows film particle noise as an example, showing a part of theoutput image in FIG. 5 which is reproduced from the image data acquiredby the imaging section 1 directly without subjecting it to any blurringprocess. To produce this image, the image data acquired by the imagingsection 1 is enlarged and cropped near the inner end of the left eye. InFIG. 8, film particle noise is visible on the skin as fine, particulatevariations of luminosities. Film particle noise of this form appears asa coarse look across the entire image in FIG. 5.

To determine the noise removing rates for chromaticity noise andluminosity noise, the noise-removing-rate computing section 7 includes adistribution parameter computing section 9, achromaticity-noise-removing-rate computing section 10, aluminosity-noise-removing-rate computing section 11, and a referencespecification section 12.

The distribution parameter computing section 9 computes a distributionparameter DP of the luminosity data YY_(xy) fed from the Y/C separatorsection 6 of each unit area to obtain variations of the luminosity dataYY_(xy).

The chromaticity-noise-removing-rate computing section 10 computes achromaticity-noise-removing-ratio parameter RC from the distributionparameter DP fed from the distribution parameter computing section 9.The chromaticity-noise-removing-ratio parameter RC is a parameterdictating how much of the chromaticity data BY_(xy), RY_(xy) of thetarget pixel is to be replaced with the mean values of the chromaticitydata BY_(xy), RY_(xy) over the unit area including that target pixel.

The luminosity-noise-removing-rate computing section 11 computes aluminosity-noise-removing-ratio parameter RD from thechromaticity-noise-removing-ratio parameter RC fed from thechromaticity-noise-removing-rate computing section 10. Theluminosity-noise-removing-ratio parameter RD is a parameter dictatinghow much of the luminosity data YYXy of the target pixel is to bereplaced with the mean values of the luminosity data YYXy over the unitarea including that target pixel.

The reference specification section 12 specifies a first reference valueT₁ and a second reference value T₂ (will be detailed later) of thedistribution parameter DP and supplies the first reference value T₁ tothe chromaticity-noise-removing-rate computing section 10 and the secondreference value T₂ to the luminosity-noise-removing-rate computingsection 11.

The first reference value T₁ serves as a reference by which an area isdetermined where no blurring is applied at all to chromaticity noise orluminosity noise (will be detailed later). Meanwhile, the secondreference value T₂ serves a reference by which an area is determinedwhere chromaticity noise is removed, but luminosity noise is notremoved. Both the first and second reference values T₁, T₂ are variablewith an input to the reference specification section 12 if necessary.

The noise removing section 8 includes a mean value computing section 13,a chromaticity noise removing section 14, and a luminosity noiseremoving section 15.

The mean value computing section 13 computes mean values of chromaticitydata BY_(xy), RY_(xy) and luminosity data YY_(xy) over each unit areaand outputs the results as mean chromaticity data BY_(av), RY_(av) andmean luminosity data YY_(av).

The chromaticity noise removing section 14 receives the chromaticitydata BY_(xy), RY_(xy) from the Y/C separator section 6, the meanchromaticity data BY_(av), RY_(av) from the mean value computing section13, and the chromaticity-noise-removing-ratio parameter RC from thechromaticity-noise-removing-rate computing section 10, and replaces thechromaticity data BY_(xy), RY_(xy) with the mean chromaticity dataBY_(av), RY_(av) at a rate dictated by thechromaticity-noise-removing-ratio parameter RC, so as to outputreplacement chromaticity data BY_(xy)′, RY_(xy)′. For some values of thechromaticity-noise-removing-ratio parameter RC, the chromaticity noiseremoving section 14 does not perform blurring (replacement) at all andsimply passes on the chromaticity data BY_(xy), RY_(xy) for output.

The luminosity noise removing section 15 receives the luminosity dataYY_(xy) from the Y/C separator section 6, the mean luminosity dataYY_(av) from the mean value computing section 13, and theluminosity-noise-removing-ratio parameter RD fromluminosity-noise-removing-rate computing section 11, and replaces theluminosity data YY_(xy) with the mean luminosity data YY_(av) at a ratedictated by the luminosity-noise-removing-ratio parameter RD, so as tooutput replacement luminosity data YY_(xy). For some values of theluminosity-noise-removing-ratio parameter RD, the luminosity noiseremoving section 15 does not perform blurring (replacement) at all andsimply passes on the luminosity data YY_(xy) for output.

The following will specifically describe how the film particle noise isremoved by the foregoing structure. According to the present invention,the imaging section 1 creates the BGR sets of image data from a negativefilm and the Y/C separator section 6 separates them into thechromaticity data BY_(xy), RY_(xy) and the luminosity data YY_(xy).Then, the noise removing section 8 removes film particle noise from thedata BY_(xy), RY_(xy), and YY_(xy). In other words, film particle noiseis contained in each of the BGR sets of image data which is separatedinto the chromaticity noise and the luminosity noise; the film particlenoise is removed from both the chromaticity noise and the luminositynoise.

To retain edges in the image, edges are first identified on the basis ofvariations of the luminosity data YY_(xy). Blurring should not appliedat all to the edges and should be increasingly strong upon moving awayfrom the edges, i.e., moving close to the monotonous parts of the imagewhere luminosity and chromaticity vary by only small amounts. Inaddition, in those areas where blurring is implemented, the chromaticitynoise should be relatively thoroughly removed, while the luminositynoise should be relatively partially removed. The noise-removing-ratecomputing section 7 computes such a chromaticity-noise-removing-ratioparameter RC and a luminosity-noise-removing-ratio parameter RD that canestablish an algorithm implementing the blurring.

The variations of the luminosity data YY_(xy) are represented by thedistribution parameter DP for each unit area enclosing 7×7 pixels as inFIG. 3. The distribution parameter DP is given by $\begin{matrix}{{{D1} = {\sum\limits_{i = {x - 3}}^{x + 3}{\sum\limits_{i = {y - 3}}^{y + 3}{YY}_{ij}}}}{{D2} = {\sum\limits_{i = {x - 3}}^{x + 3}{\sum\limits_{i = {y - 3}}^{y + 3}{{YY}_{ij} \times {YY}_{ij}}}}}} & \left\lbrack {{Eq}.\quad A} \right\rbrack \\{{DP} = {\left\{ {{D2} - {\left( {{D1} \times {D1}} \right)/49}} \right\}/49}} & \left\lbrack {{Eq}.\quad B} \right\rbrack\end{matrix}$and the computation is done by the distribution parameter computingsection 9.

These two equations are devised for a practical purpose of quickcomputation and give only an approximate value of the distributionparameter DP. Theoretically, strictly in line with the definition ofdistribution, the equations are written:X _(av) =ΣXi/N  [Eq. 1]DP=Σ(Xi−X _(av))² /N  [Eq. 2]where N is the number of pixels in a unit area.

The distribution parameter DP increases greatly when there are largeluminosity variations among the 49 pixels in the unit area, because thecomputation involves raising to the second power in Equation 2.Chromaticity variations and luminosity variations are either very smallor practically ignorable in monotonous parts of the image and relativelylarge at edges in the image; the latter variations are particularlylarge at edges. Therefore, if a unit area has a large distributionparameter DP computed as a representation of variations of theluminosity data YY_(xy), the unit area can be regarded as being locatedat, or closely to, an edge in the image.

Accordingly, to achieve an objective of the present invention that noblurring be implemented at edges in an image, a threshold value shouldbe specified for the distribution parameter DP so that blurring isprohibited in those unit areas where the distribution parameter DP isgreater than, or equal to, the threshold value. The threshold value isspecified by the reference specification section 12 as the firstreference value T₁.

To achieve another objective of the present invention that blurringbecome increasingly strong as moving away from the edges, thechromaticity data BY_(xy), RY_(xy) and the luminosity data YY_(xy) ofthe target pixel located in the middle of the unit area should bereplaced with the respective mean values of the 49 pixels in the unitarea at rates that increase as moving away from the edges.

To achieve another objective of the present invention that in thoseareas where blurring is implemented, the chromaticity noise should berelatively thoroughly removed, while the luminosity noise should berelatively partially removed. The rates at which the chromaticity dataBY_(xy), RY_(xy) is replaced with associated mean values should bespecified greater than the rate at which the luminosity data YY_(xy) isreplaced with an associated mean value.

In the present invention, the reference specification section 12specifies the second reference value T₂ so that it is smaller than thefirst reference value T₁, wherein the chromaticity noise is removed at arelatively large rate and the luminosity noise is removed at arelatively small rate in those unit areas where the distributionparameter DP is smaller than the second reference value T₂, and thechromaticity noise is removed, but the luminosity noise is not removed,in those unit areas where the distribution parameter DP is greater thanthe second reference value T₂.

FIG. 4 shows a graphical representation of the algorithm as an example.The first reference value T₁ is set to 300. The second reference valueT₂ is set to 120. The chromaticity-noise-removing-ratio parameter RC isgiven byRC=DP/300 (if RC>1, RC=1)  [Eq. 3]The luminosity-noise-removing-ratio parameter RD is given byRD=RC+0.6 (if RD>1, RD=1)  [Eq. 4]

The chromaticity-noise-removing-ratio parameter RC is such a variablethat determines the replacement ratio on the basis of a linear ratio:specifically, when the chromaticity-noise-removing-ratio parameter RCequals 0, the chromaticity data BY_(xy), RY_(xy) is replaced with theassociated mean values at a rate of 1, that is, replaced completely, andwhen it equals 1, the chromaticity data BY_(xy), RY_(xy) is replacedwith the mean value at a rate of 0, that is, retained completely.

The luminosity-noise-removing-ratio parameter RD is defined similarly sothat luminosity noise removal is implemented on the basis of the samelinear ratio as the chromaticity noise removal for the distributionparameter DP ranging from 0 to the second reference value T₂ (120): theluminosity-noise-removing-ratio parameter RD is set to 0.6 when thedistribution parameter DP equals 0. The definition is based onexperimental results that images printed on photographic printing paperhad a desirable feel when the luminosity data YYXy was replaced with themean value in those unit areas where the distribution parameter DP isfrom 0 120 in such a way that the replacement ratio does not exceed 0.4(=1−0.6).

In the algorithm, the parameters RC, RD are computed by thechromaticity-noise-removing-rate computing section 10 and theluminosity-noise-removing-rate computing section 11 respectively. Thechromaticity noise removing section 14 receives the chromaticity dataBY_(xy), RY_(xy) from the Y/C separator section 6, the mean chromaticitydata BY_(av), RY_(av) from the mean value computing section 13, and thechromaticity-noise-removing-ratio parameter RC from thechromaticity-noise-removing-rate computing section 10, and computesreplacement chromaticity data BY_(xy)′, RY_(xy)′ according to theequation:BY _(xy) ′=BY _(av)×(1−RC)+BY _(xy) ×RCRY _(xy) ′=RY _(av)×(1−RC)+RY _(xy) ×RCChromaticity noise is removed from the replacement chromaticity dataBY_(xy)′, RY_(xy)′.

The luminosity noise removing section 15 receives the luminosity dataYY_(xy) from the Y/C separator section 6, the mean luminosity dataYY_(av) from the mean value computing section 13, and theluminosity-noise-removing-ratio parameter RD from theluminosity-noise-removing-rate computing section 11, and computesreplacement luminosity data YY_(xy)′ according to the equation:YY _(xy) ′=YY _(av)×(1−RD)+YY _(xy) ×RD  [Eq. 5]Luminosity noise is removed from the replacement luminosity dataYY_(xy)′.

The mean chromaticity data BY_(av), RY_(av) and the mean luminosity dataYY_(av) are calculated by the mean value computing section 13 accordingto the equations: $\begin{matrix}{{{BY}_{av} = {\sum\limits_{i = {x - 3}}^{x + 3}{\sum\limits_{i = {y - 3}}^{y + 3}{{BY}_{ij}/49}}}}{{RY}_{av} = {\sum\limits_{i = {x - 3}}^{x + 3}{\sum\limits_{i = {y - 3}}^{y + 3}{{RY}_{ij}/49}}}}{{YY}_{av} = {\sum\limits_{i = {x - 3}}^{x + 3}{\sum\limits_{i = {y - 3}}^{y + 3}{{YY}_{ij}/49}}}}} & \left\lbrack {{Eq}.\quad C} \right\rbrack\end{matrix}$

Now, the operation of the blurring section 2 based on equations 1-5 willbe described in detail. Let us take the luminosity data exampleinvolving 3×3 pixels introduced in the Background of the Inventionsection above for convenience.

Suppose that the Y/C separator section 6 produces the followingluminosity data YY_(xy) from the BGR image data fed from the imagingsection 1: 51 49 53 52 50 49 48 51 47

in a 3×3-pixel unit area in a monotonous part of an image; 10 30 70 1550 90 20 80 85

in a 3×3-pixel unit area at an edge in the image; and 45 49 45 49 74 4945 49 45in a 3×3-pixel unit area in a monotonous part, of the image, whichcontains film particle noise.

The mean value computing section 13 computes mean luminosity dataYY_(av) according to equation 1 for each unit area. Results areYY_(av)(A)=50, YY_(av)(B)=50, and YY_(av)(C)=50, for the monotonous partA, the edge B, and the monotonous part C with noise respectively.

Next, the distribution parameter computing section 9 computes adistribution parameter DP from the mean luminosity data YY_(av) fed fromthe mean value computing section 13 and the luminosity data YY_(xy) fedfrom the Y/C separator section 6 according to equation 2 for each unitarea. Results are DP(A)=3.3, DP(B)=916.7, and DP(C)=75.6. Note that asmentioned in the foregoing, in actual practice, the distributionparameter computing section 9 computes distribution parameters DPaccording to equation A for quick computation.

Then, the chromaticity-noise-removing-rate computing section 10 computesa chromaticity-noise-removing-ratio parameter RC from the distributionparameter DP fed from the distribution parameter computing section 9according to equation 3 for each unit area. Results are RC(A)=0.01,RC(B)=1, and RC(C)=0.25.

The luminosity-noise-removing-rate computing section 11 computes aluminosity-noise-removing-ratio parameter RD from thechromaticity-noise-removing-ratio parameter RC fed from thechromaticity-noise-removing-rate computing section 10 according toequation 4 for each unit area. Results are RD(A)=0.61, RD(B)=1, andRD(C)=0.85.

Finally, the luminosity noise removing section 15 computes replacementluminosity data YY_(xy) for the target pixel from the luminosity dataYY_(xy) fed from the Y/C separator section 6, the mean luminosity dataYY_(av) fed from the mean value computing section 13, and theluminosity-noise-removing-ratio parameter RD fed from theluminosity-noise-removing-rate computing section 11 according toequation 5 for each unit area, so as to replace the luminosity dataYY_(xy) of the target pixel with the replacement luminosity dataYY_(xy)′. All the pixels are subjected to this process until all theluminosity data YY_(xy) is replaced with replacement luminosity dataYY_(xy)′ (Step 9 in FIG. 12).

The target pixel in the foregoing monotonous part of the image hasluminosity data YY_(xy)=50 and computed replacement luminosity dataYY_(xy)′=50, which happen to be identical. The original luminosity datadoes not change in the process, and the resulting luminosity data is 5149 53 52 50 49 48 51 47Monotonous parts inherently do not require much effective blurring.

Further, at the edges of an image, since theluminosity-noise-removing-ratio parameter RD equals 1, the replacementratio for the mean luminosity data YY_(av) is 0, completely retainingthe original luminosity data YY_(xy). Consequently, in the blurringprocess of the present invention, the non-edge parts of the image areblurred, i.e., the noise is removed, but the edges are not affected andthe image retains its contrast.

Likewise, in monotonous parts with noise, the target pixel hasluminosity data YY_(xy)=74 and replacement luminosity data YY_(xy)′=70computed according to equation 5. The resulting luminosity data is 45 4945 49 70 49 45 49 45The distribution parameter DP(C) computed is 55.8, which shows that theluminosity data YY_(xy) is now more uniform than before thetransformation and that the noise peak has been attenuated. Noise hasbeen successfully reduced. In the actual processing, the target pixelwith luminosity data YY_(xy)=74 is not the only pixel affected, but theadjacent pixels are also subjected to the same procedures, one by one,to replace luminosity data YY_(xy) with replacement luminosity dataYY_(xy)′. The actual distribution parameter DP(C) is therefore farsmaller.

More noise is removed in the above example, if the second referencevalue T₂ is set to a value larger than 120. For example, setting thesecond reference value T₂ to 180, equation 4 is writtenRD=RC+0.4

and RD(C)=0.65. Using this RD, replacement luminosity data YY_(xy)′ isobtained: 45 49 45 49 66 49 45 49 45The distribution parameter DP (C) computed from the data equals 39.2,which shows that film particle noise is now less visible.

FIG. 5 to FIG. 10 show results of the foregoing image processing inaccordance with present invention applied to the image data read by theimaging section 1.

FIG. 5 shows, as mentioned earlier, an output of the image data that isread by the imaging section 1 and passed on to the exposure section 5with no noise removing process implemented at all. The output is nodifferent from the original image.

FIG. 6 shows an output of the image data that is read by the imagingsection 1 and subjected to chromaticity noise removal before being fedto the exposure section 5.

FIG. 7 shows an output of the image data that is read by the imagingsection 1 and subjected to both chromaticity noise removal andluminosity noise removal before being fed to the exposure section 5.

A comparison of FIGS. 5-7 shows that the facial skin and the fabric ofclothes appear coarse in FIG. 5 (original image), but less so in FIG. 6and even less so in FIG. 7. Meanwhile, edge sharpness of the eyes, nose,body, etc. does not distinctly differ among FIGS. 5-7.

For better comparison on the film particle level, FIGS. 8-10 show outputresults of the same image data as used for FIGS. 5-7, but enlarged andcropped near the inner end of the left eye, for better comparison atfilm particle levels. The output results confirm that the film particlenoise, a cause for the coarse look in the image, is gradually removedfrom FIG. 8 to FIG. 9 and to FIG. 10 and that edges appear littleaffected by the processing and are almost perfectly retained in FIGS. 6and 7.

The foregoing noise removal, capable of retaining edges in the image, isimplemented by a program stored on a recording medium that is readableby a computer. In the present invention, the recording medium (notshown) may be a memory, for example, a ROM, required for the imageprocessing section 4 in FIG. 2 to execute the process or a programmedium that is readable when inserted in an external reader device.

In either case, the recorded program may be adapted so that it isaccessible and executable by a microprocessor (not shown) or that it ispreinstalled in the main device and ready for readout and loading into aprogram memory area (not shown) in the image processing section 4 whereit is executed.

The program medium may be adapted to be separable from the main device.It may be a nonvolatile medium: namely, a tape, such as a magnetic tapeor a cassette tape; a magnetic disk, such as a floppy disk or a harddisk; an optical disk, such as a CD-ROM, an MO disk, an MD, or a DVD; acard, such as a memory or IC card or an optical card; or a semiconductormemory, such as a mask ROM, an EPROM, an EEPROM, or a flash ROM.

The system of the present invention is configured to connect to theInternet and other communications networks; the program medium maytherefore be a volatile transmission medium to which the program isdownloaded over a communications network when necessary. In this case,the program to be downloaded may be preinstalled in the main device orinstalled from a different recording medium when necessary.

The content of the recording medium is not limited to a program and mayinclude data.

As described so far, an image processing method in accordance with thepresent invention includes the steps of:

-   -   separating image data into luminosity data and chromaticity data        (Step 1 in FIG. 12); and    -   changing a rate of smoothing of the chromaticity data and a rate        of smoothing of the luminosity data according to a variation of        the luminosity data in two-dimensional coordinate space.

Another image processing method in accordance with the present inventionincludes the features of this method and may be such that:

-   -   a first reference value (T₁) is specified as to a degree of the        variation of the luminosity data (distribution parameter DP)        (Step 2 in FIG. 12); and    -   in image areas where the variation of the luminosity data (DP)        is smaller than the first reference value (T₁) (T₁>DP, Step 3 in        FIG. 12), the chromaticity data is subjected to the smoothing        first (Step 4 in FIG. 12) and, if necessary, the luminosity data        is subjected to the smoothing thereafter (Step 6 in FIG. 12).

With these methods, those areas located close to edges are identifiedusing the first reference value, since the image areas where thevariation of the luminosity data is larger than the first referencevalue are located closer to edges than to monotonous parts in the imageand the areas where the variation of the luminosity data is smaller thanthe first reference value are located closer to monotonous parts than toedges in the image.

Therefore, a priority is given to the smoothing of the chromaticity datawhich is relatively impervious to edge information attenuation, ratherthan to the smoothing of the luminosity data which is relativelysusceptible to edge information attenuation, near monotonous parts. Therate of the luminosity noise removal can be rendered smaller ifchromaticity noise is removed beforehand than if not. In short, thesmoothing of the luminosity data is selectively done when only it iseffective. This produces better results in both the retainment of edgesand the reduction of a coarse look of the image.

A further image processing method in accordance with the presentinvention includes the features of the foregoing method and may be suchthat:

-   -   a first reference value (T₁) is specified as to a degree of the        variation of the luminosity data (DP) (Step 2 in FIG. 12); and    -   in image areas where the variation of the luminosity data (DP)        is smaller than the first reference value (T₁) (T₁>DP, Step 3 in        FIG. 12), the rate of the smoothing of the chromaticity data is        made greater than the rate of the smoothing of the luminosity        data (Step 6 in FIG. 12).

With this method, those areas located close to edges are identifiedusing the first reference value. Therefore, near monotonous parts,setting the rate of the smoothing of the chromaticity data which isrelatively impervious to edge information attenuation smaller than therate of the smoothing of the luminosity data which is relativelysusceptible to edge information attenuation produces better results inboth the retainment of edges and the reduction of a coarse look of theimage.

A still further image processing method in accordance with the presentinvention includes the features of the foregoing method and may be suchthat:

-   -   a second reference value (T₂) is specified as to a degree of the        variation of the luminosity data (DP) (Step 2 in FIG. 12) so        that the second reference value (T₂) is smaller than the first        reference value (T₁); and    -   in image areas where the variation of the luminosity data (DP)        is larger than the second reference value (T₂) (DP>T₂, Step 5 in        FIG. 12), the luminosity data is not subjected to the smoothing        (Step 7 in FIG. 12).

With this method, the specification of the first and second referencevalues enables the image to be divided into those areas close tomonotonous parts, those areas close to edges, and the middle areasrelatively far from both the monotonous parts and the edges, since thoseareas close to the monotonous parts are further divided into two groupsaccording to whether the variation of the luminosity data is smallerthan the second reference value or not.

Removing no noise from the luminosity data which is relativelysusceptible to edge information attenuation in those areas where thevariation of the luminosity data is larger than the second referencevalue produces better results in the retainment of the edges in theimage.

Meanwhile, removing noise from the chromaticity in at least those areaswhere the variation of the luminosity data is smaller than the firstreference value as described in the foregoing produces good results inthe reduction of a coarse look of the image.

A further image processing method in accordance with the presentinvention includes the features of the foregoing method and may be suchthat

-   -   in image areas where the variation of the luminosity data (DP)        is larger than the first reference value (T₁) (DP>T₁, Step 3 in        FIG. 12), the luminosity data is not subjected to the smoothing        and the chromaticity data is not subjected to the smoothing        (Step 8 in FIG. 12).

With this method, the edges in the image are retained in an optimummanner, since no noise is removed from the luminosity data and thechromaticity data in those areas where the variation of the luminositydata is larger than the first reference value, that is, those areaslocated close to edges in the image.

Still another image processing method in accordance with the presentinvention includes the features of the foregoing method and may be suchthat

-   -   the rate of the smoothing of the chromaticity data and the rate        of the smoothing of the luminosity data are changed according to        a distribution parameter of the luminosity data.

In this method, the distribution parameter of the luminosity data iseasily computable and still faithfully represents variations of theluminosity data: the distribution parameter is 0 if the luminosity datahas no variation at all and takes an increasingly large positive valuewhen the variation of the luminosity data increases starting from 0.

Therefore, the distribution parameter computed for the luminosity dataenables easy discrimination, for example, among those areas close tomonotonous parts, those areas close to edges, and the middle areasrelatively far from both the monotonous parts and the edges.

Using the distribution parameter of the luminosity data, the balance canbe easily optimized between the chromaticity noise removal and theluminosity noise removal. The distribution parameter is obtained byraising to the second power and then averaging the difference betweenthe mean value of the luminosity data and the mean value of theluminosity data; the noise removal using the distribution parameterimparts a very natural look to the image, presumably, because thecomputation involves raising to the second power. Besides, thecomputation is simple and quick and makes great contributions toimplement the image processing method by hardware.

An image processing device in accordance with the present inventionincludes:

-   -   (1) a data separator section for separating image data into        luminosity data and chromaticity data;    -   (2) a chromaticity noise removing section for smoothing the        chromaticity data;    -   (3) a luminosity noise removing section for smoothing the        luminosity data; and    -   (4) a smoothing rate computing section for computing a variation        of the luminosity data in two-dimensional coordinate space and        computing, for each unit area of an image, a rate of the        smoothing of the chromaticity data and a rate of the smoothing        of the luminosity data according to the variation as outputs to        the chromaticity noise removing section and the luminosity noise        removing section respectively.

Another image processing device in accordance with the present inventionincludes the features of the foregoing configuration and may be suchthat

-   -   the smoothing rate computing section compares the variation of        the luminosity data with a first reference value specified as to        a degree of the variation of the luminosity data, and in image        areas where the variation of the luminosity data is smaller than        the first reference value, computes the rates given by such        equations that the rate of the smoothing of the chromaticity        data becomes larger than the rate of the smoothing of the        luminosity data.

With this configuration, the image processing device produces betterresults in both the retainment of edges and the reduction of a coarselook of the image.

A further image processing device in accordance with the presentinvention includes the features of the foregoing configuration and maybe such that

-   -   the smoothing rate computing section compares the variation of        the luminosity data with a second reference value specified as        to a degree of the variation of the luminosity data so that the        second reference value is smaller than the first reference        value, and in image areas where the variation of the luminosity        data is larger than the second reference value, computes the        rates given by such equations that the luminosity data is not        subjected to the smoothing.

With this configuration, the image processing device produces betterresults in the retainment of edges and produces as good results in thereduction of a coarse look of the image.

A still further image processing device in accordance with the presentinvention includes the features of the foregoing configuration and maybe such that

-   -   in image areas where the variation of the luminosity data is        larger than the first reference value, the smoothing rate        computing section computes the rates given by such equations        that the luminosity data is not subjected to the smoothing and        the chromaticity data is not subjected to the smoothing.

With this configuration, the edges in the image are retained in anoptimum manner.

Yet another image processing device in accordance with the presentinvention includes the features of the foregoing configuration and maybe such that the smoothing rate computing section includes a referencespecification section for assigning variable values to the referencevalues depending on an external input.

With this configuration, neither the first reference value nor thesecond reference value is fixed, but are varied by the referencespecification section; therefore, the reference values can be selected,while checking the quality of the resultant image, so that optimumbalanced is obtained between the retainment of edges and the reductionof a coarse look of the image.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art intended tobe included within the scope of the following claims.

1. An image processing method, comprising the steps of: separating imagedata into luminosity data and chromaticity data; and changing a rate ofsmoothing of the chromaticity data and a rate of smoothing of theluminosity data according to a variation of the luminosity data intwo-dimensional coordinate space.
 2. The image processing method asdefined in claim 1, wherein the rate of the smoothing of thechromaticity data and the rate of the smoothing of the luminosity dataare changed according to a distribution parameter of the luminositydata.
 3. The image processing method according to claim 1, wherein therate of the smoothing of the chromaticity data is computed from adistribution of the luminosity data; and the rate of the smoothing ofthe luminosity data is computed from the rate of smoothing of thechromaticity data.
 4. An image processing device, comprising: a dataseparator section for separating image data into luminosity data andchromaticity data; a chromaticity noise removing section for smoothingthe chromaticity data; a luminosity noise removing section for smoothingthe luminosity data; and a smoothing rate computing section forcomputing a variation of the luminosity data in two-dimensionalcoordinate space and computing, for each unit area of an image, a rateof the smoothing of the chromaticity data and a rate of the smoothing ofthe luminosity data according to the variation as outputs to thechromaticity noise removing section and the luminosity noise removingsection respectively.
 5. The image processing device according to claim4, wherein the rate of the smoothing of the chromaticity data iscomputed from a distribution of the luminosity data; and the rate of thesmoothing of the luminosity data is computed from the rate of smoothingof the chromaticity data.
 6. A computer-readable medium, for recordingan image processing program, performing a process of: separating imagedata into luminosity data and chromaticity data; and changing a rate ofsmoothing of the chromaticity data and a rate of smoothing of theluminosity data according to a variation of the luminosity data intwo-dimensional coordinate space.
 7. The computer-readable medium asdefined in claim 6, wherein: a first reference value is specified as toa degree of the variation of the luminosity data; and in image areaswhere the variation of the luminosity data is smaller than the firstreference value, the chromaticity data is subjected to the smoothingfirst and, if necessary, the luminosity data is subjected to thesmoothing thereafter.
 8. The computer-readable medium as defined inclaim 7, wherein: a second reference value is specified as to the degreeof the variation of the luminosity data so that the second referencevalue is smaller than the first reference value; and in image areaswhere the variation of the luminosity data is larger than the secondreference value, the luminosity data is not subjected to the smoothing.9. The computer-readable medium as defined in claim 7, wherein in imageareas where the variation of the luminosity data is larger than thefirst reference value, the luminosity data is not subjected to thesmoothing and the chromaticity data is not subjected to the smoothing.10. The computer-readable medium as defined in claim 6, wherein: a firstreference value is specified as to a degree of the variation of theluminosity data; and in image areas where the variation of theluminosity data is smaller than the first reference value, the rate ofthe smoothing of the chromaticity data is made greater than the rate ofthe smoothing of the luminosity data.
 11. The computer-readable mediumas defined in claim 10, wherein: a second reference value is specifiedas to the degree of the variation of the luminosity data so that thesecond reference value is smaller than the first reference value; and inimage areas where the variation of the luminosity data is larger thanthe second reference value, the luminosity data is not subjected to thesmoothing.
 12. The computer-readable medium as defined in claim 10,wherein in image areas where the variation of the luminosity data islarger than the first reference value, the luminosity data is notsubjected to the smoothing and the chromaticity data is not subjected tothe smoothing.
 13. The computer-readable medium as defined in claim 6,wherein the rate of the smoothing of the chromaticity data and the rateof the smoothing of the luminosity data are changed according to adistribution parameter of the luminosity data.
 14. The computer-readablemedium according to claim 6, wherein the rate of the smoothing of thechromaticity data is computed from a distribution of the luminositydata; and the rate of the smoothing of the luminosity data is computedfrom the rate of smoothing of the chromaticity data.
 15. A computer datasignal embodied in a carrier wave and representing a series ofinstructions which cause a computer to perform an image processingmethod, the image processing method comprising the steps of: separatingimage data into luminosity data and chromaticity data; and changing arate of smoothing of the chromaticity data and a rate of smoothing ofthe luminosity data according to a variation of the luminosity data intwo-dimensional coordinate space.
 16. The computer data signal accordingto claim 15, wherein the rate of the smoothing of the chromaticity datais computed from a distribution of the luminosity data; and the rate ofthe smoothing of the luminosity data is computed from the rate ofsmoothing of the chromaticity data.